Ok, pci=noacpi and acpi=off don't fix the issue. Instead, 'acpi=off' turns the soft lockup into a full-blown kernel panic.
Removing the nvidia stuff now. Not expecting much of it since the 'tainted' flag wasn't set during that kernel panic, suggesting that it hadn't loaded yet. Nonetheless .. -- [feisty] [linux-image-2.6.19-6] BUG: soft lockup detected on CPU#0! https://launchpad.net/bugs/72895 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs